Rework setting image tags to support PRs better

[webbnh]

Changes introduced with this PR

This PR reworks the reusable workflow which builds plugin container images. It combines into one all the steps which handle different cases of generating container image tags depending on the CI trigger. And, if the trigger is a Pull Request, it uses the name of the PR branch instead of the name of the GitHub "ref" (which is usually something generic, like 17/merge). And, it picks a few bits of lint.

So, the tags will now be one of the following:

• releases: release and latest [this is unchanged]
• the main branch: main_latest [this is unchanged]
• PRs: <PR_branch_name>_<last_commit_hash> [this is new]
• tags and other branches: <tag-name_or_branch-ref>_<commit_hash> [this is unchanged]

This PR was tested using arcalot/arcaflow-plugin-rtla#5 for PR builds and for tag builds, and it will use arcalot/arcaflow-plugin-rtla#4 for testing main builds (i.e., once this PR is merged, then that one can be merged, and then this one will get tested 🙂).

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[dbutenhof]

Yeah, OK, this seems plausible, although I kinda wish it was easier to follow this in the workflow log. (But the values on Quay look fine, so the IMAGE_TAGS setting clearly propagated to the action and did what we expected.)

[webbnh]

I kinda wish it was easier to follow this in the workflow log.

Yeah; I did make it show its work (ditto) for you, though.

[webbnh]

it will use arcalot/arcaflow-plugin-rtla#4 for testing main builds (i.e., once this PR is merged, then that one can be merged, and then this one will get tested 🙂).

And, it did, and it worked!